The Circular Flow of Income

The Circular Flow of Income

The circular flow of income model illustrates the movement of income, spending, and output within an economy, involving households, firms, and the government. It assumes that output generates income, which is subsequently spent on output. This explains why a country's GDP can be measured through its output, income, and expenditure.

Economists use four simplified models to understand this flow:

  1. 2 Sector Economy

  2. 3 Sector Economy

  3. Open Economy

  4. Open Economy without a Government

2 Sector Economy

This is the simplest economy, comprising only households and firms. It's also known as a closed economy without government.

  • Households: Own the factors of production.

  • Firms: Utilize these factors.

The circular flow means that money is paid to factors of production in exchange for their services. The owners of these factors then spend this money on goods and services.

In this model:

  • Households supply factors of production and receive income from firms.

  • They spend this income (consumption) to acquire goods and services.

Any money removed from this cycle is a withdrawal/leakage, reducing the circular flow. Money added is an injection, increasing the circular flow.

  • Withdrawals/Leakages (W): Reduce GDP.

  • Injections (J): Increase GDP.

Households often save a portion of their income, which is not consumed.

  • Saving: Part of household income not spent, a withdrawal (W).

Firms invest money earned from sales, adding to the circular flow.

  • Investment: Expenditure by firms, an injection (I).

Some expenditure is additional to spending derived from domestic output's income.

Equilibrium in a 2 Sector Economy

Equilibrium is achieved when income (Y) equals aggregate expenditure (AE).

Y = C + S
AE = C + I

Where:

  • C = Consumption by households

  • S = Savings

  • I = Investment by firms

Therefore, in equilibrium:

Y = AE
C + S = C + I

This simplifies to:

I = S

Macroeconomic equilibrium exists when:

  1. Income equals aggregate expenditure.

  2. Injections equal withdrawals.

3 Sector Economy

This economy includes the government sector. It's also called a closed economy with government or a closed mixed economy.

The government injects spending (G) into the circular flow but also levies taxes (T), which are withdrawals.

  • Government Spending (G): Injection.

  • Taxes (T): Withdrawal.

Equilibrium in a 3 Sector Economy

Y = C + S + T
AE = C + I + G

In equilibrium:

Y = AE
C + S + T = C + I + G

Alternatively, equilibrium is when:

Injections (J) = Withdrawals (W)
I + G = S + T

Open Economy

This economy includes the international sector, introducing exports (X) and imports (M).

  • Imports (M): Purchases of foreign goods, a withdrawal.

  • Exports (X): Sales of domestic goods to foreign economies, an injection.

Equilibrium in an Open Economy

AE = C + I + G + X
Y = C + S + T + M

In equilibrium:

Y = AE
C + S + T + M = C + I + G + X

Alternatively, equilibrium is when:

Injections (J) = Withdrawals (W)
I + G + X = S + T + M

Open Economy without Government

This is similar to the open economy but excludes the government sector. There are no government spending or taxation components.

Equilibrium in an Open Economy without Government

AE = C + I + X
Y = C + S + M

In equilibrium:

Y = AE
C + S + M = C + I + X

Alternatively, equilibrium is when:

Injections = Withdrawals
I + X = S + M

Equilibrium and Disequilibrium

For income to remain constant, injections must equal leakages.

Equilibrium occurs when Y = AE or J = W. However, this is not the same as full employment equilibrium. J = W doesn't guarantee full employment or stable prices. The economy can be in equilibrium with unemployment or inflation.

A disequilibrium occurs when injections exceed withdrawals (J > W) or withdrawals exceed injections (J < W). These disequilibria are temporary, and the economy will correct itself.

  • J > W: Economy grows.

  • J < W: Economy shrinks.

If injections exceed leakages, extra spending causes income to rise, increasing the economy's size. If leakages exceed injections, spending decreases, and income falls, shrinking the economy.

At Y1, injections are greater than withdrawals, causing investments to exceed savings. Households consume a greater proportion of their income, leading to shortages. Firms expand production, increasing incomes and savings until equilibrium is reached.

At Y2, withdrawals exceed injections, causing savings to be greater than investment. Unsold products lead to reduced production and incomes until equilibrium is restored.

Changes in Injections and Withdrawals

Changes in injections and withdrawals cause shifts in their respective curves, affecting the equilibrium level of national income. In a 2 sector closed economy, increased investment shifts the injection curve upwards, raising GDP. Decreased investment shifts the injection curve downwards, lowering GDP.

The same principles apply to changes in government spending and imports.

In a four-sector economy, equilibrium occurs where investment (I) + government spending (G) + exports (X) = saving (S) + taxation (T) + imports (M).

Increased government spending on infrastructure leads to injections exceeding withdrawals, causing an upward shift in the injection curve and an increase in national income. Higher incomes lead to increased saving, income tax, and spending on imports, eventually restoring equilibrium.

Increased imports cause withdrawals to exceed injections, leading to a leftward shift in the withdrawal curve. Households spend more on international goods, decreasing demand for domestic goods. Firms reduce output, decreasing GDP and national income.

If tax rates rise without changes in government spending, households and firms have less available for spending. Increased saving also causes GDP to fall in the short run.

Example

To determine if an economy is in equilibrium, use the formulas Y = AE or I + G + X = S + T + M.

For example, in an economy:

  • A: C = 450, I = 200, G = 400, X = 400, S = 100, T = 200, M = 150

  • B: C = 1000, I = 200, G = 400, X = 400, S = 250, T = 500, M = 250

Economy A is not in equilibrium. Whereas economy B I + G + X = S + T + M; therefore, the injections are equal to withdrawals, and the economy is in equilibrium.

Links Between Injections and Leakages

In the long run, changes in injections and leakages are interconnected. Increased investment raises incomes, leading to more savings, which can finance more investment. Higher government spending may increase tax revenue, and greater exports also increase incomes, leading to increased spending on both domestic and imported products.

An injection will cause GDP to increase until leakages rise to match the total injections.